1. Field of the Invention
The present invention relates to stereolithographic apparatus and method for optically manufacturing a three-dimensional object by using photohardenable resin, and particularly the present invention relates to stereolithographic apparatus and method for exposing the overall surface of a photohardenable resin layer to light through a mask at a time to optically manufacture a three-dimensional object, and also to stereolithographic apparatus and method for optically manufacturing a three-dimensional object having a complicated shape such as an overhang portion, portions which are separately mounted, plural leg portions which are different in length, or the like by using specific photohardenable resin composition. In the following description, xe2x80x9cstereolithographic processxe2x80x9d is defined as a process of exposing photohardenable resin or photohardenable resin composition to light to form a photohardened layer, and repeating the light exposing operation on photohardenable resin (composition) to laminate photohardened layers on a layer basis, thereby optically forming a desired three-dimensional object.
2. Description of the Related Art
In general, liquid photohardenable resin composition (hereinafter referred to as xe2x80x9cphotohardenable resinxe2x80x9d) has been widely used as coating (particularly, hard coating), photoresist, dental materials, etc. Recently, much attention has been paid to a so-called stereolithography technique which optically forms a three-dimensional object on the basis of data output from a controller such as a three-dimensional CAD system or the like by using photohardenable resin because a three-dimensional object can be optically formed in desired shape and size with high precision even when it has a complicated structure. With respect to the stereolithography technique, Japanese Laid-open Patent Application No. Sho-56-144478 discloses a stereolithographic method for repeating a process of applying a required amount of optical energy to liquid photohardenable resin under control to harden the photohardenable resin as a thin layer, further supplying liquid photohardenable resin onto the hardened resin layer and then exposing the liquid photohardenable resin to light controlled on the basis of stereolithographic data from a controller to harden the liquid photohardenable resin and laminate the thin hardened photohardenable resin layer on the preceding hardened resin layer, whereby a subsequent hardened photohardenable resin layer is successively laminated on a preceding hardened photohardenable resin layer to manufacture a desired three-dimensional object. Further, a practical use method of the stereolithographic method disclosed in the above publication is proposed in Japanese Laid-open Patent Application No. Sho-60-247515, and then various proposals on the stereolithography technique have been made. As a method of optically manufacturing a three-dimensional object has been generally and widely used a method of selectively irradiating laser beams such as ultraviolet laser beams or the like to the liquid surface of liquid photohardenable resin put in a stereolithographic bath under the control of a computer to harden the photohardenable resin so that a photohardened resin layer having a predetermined thickness and a desired pattern is obtained, then supplying a layer of liquid photohardenable resin onto the photohardened resin layer and then likewise exposing a laser beam such as an ultraviolet laser beam or the like to the liquid photohardenable resin layer to harden the photohardenable resin layer, and repeating the lamination/photohardening operations until a targeted three-dimensional object is obtained.
In general, it takes a long time to irradiate laser beams to a layer of photohardenable resin until the photohardenable resin layer is hardened, and for the purpose of increasing the stereolithographic process speed, an apparatus for forming a mask and irradiating the overall surface of a photohardenable resin layer through the mask pattern by an ultraviolet lamp at a time (hereinafter referred to as xe2x80x9cplane-exposurexe2x80x9d) has been proposed.
According to such a plane-exposing apparatus, a mask having a predetermined pattern formed on the surface thereof is formed and superposed on a unhardened photohardenable resin layer, and then the overall surface of the unhardened photohardenable resin layer is exposed to ultraviolet rays through the mask at a time (i.e, plane-exposed), thereby hardening the photohardenable resin layer in accordance with the mask pattern.
In the plane-exposing apparatus, however, since the mask is not brought into close contact with the unhardened photohardenable resin layer in the exposure process, uneven portions are formed on the surface of the hardened resin layer and thus it is required to cut out these uneven portions layer by layer after the hardening operation of the photohardenable resin is completed.
Furthermore, in a process of forming a photohardenable resin layer, a solid surrounding member is beforehand formed and fixed so as to surround the photohardenable resin layer, and then unhardened photohardenable resin is supplied into the inside of the fixed solid surrounding member. Therefore, unhardened photohardenable resin remains in the solid surrounding member. If the uneven portions on the surface of the hardened resin layer are cut out while the residual unhardened photohardenable resin is left, the comer portions of the hardened resin layer may be defected. In order to avoid this disadvantage, after the photohardenable resin layer is hardened, the unhardened photohardenable resin is scraped up, wax is filled into the scraped portions to prevent defects and then the uneven portions on the surface of the hardened resin layer are cut out. Therefore, extra wax, etc. are required.
Still furthermore, three-dimensional objects having complicated shapes such as overhang portions, separately-mounted portions, plural leg portions which are different in length, uneven portions, etc. have been widely manufactured by using the conventional stereolithography technique. Individual hardened layers which are successively formed by light irradiation are extremely thin, and thus a laminate obtained by laminating these thin layers is also thin. Therefore, the laminate thus finally obtained has a lower shape holding performance. In addition, photohardenable resin in a stereolithographic bath is liquid, and it has little capability of supporting a photohardened layer. Therefore, when a three-dimensional object having a complicated shape such as overhand portions, separately mounted portions, leg portions which are different in length, uneven portions or the like is manufactured, there is liable to occur such problems as hang-down, deformation, dimensional deviation, positional shift, etc. of stereolithographically-formed sites formed by photohardening during the stereolithographic process. Accordingly, in order to avoid these problems, there has been generally adopted a method of disposing a separately-formed support in a stereolithographic bath and stereolithographically forming a desired three-dimensional object while the object being formed is supported by the support (hereinafter referred to as xe2x80x9csupport basing methodxe2x80x9d), or a method of stereolithographically forming a desired three-dimensional object while an extra support portion is simultaneously formed together with the desired three-dimensional object (hereinafter referred to as xe2x80x9csupport attaching methodxe2x80x9d).
In the following description, the support-based supporting method and the support-attached supporting method will be described; in detail with reference to FIGS. 1 to 4F particularly when these methods are applied to the stereolithographic process of forming three-dimensional objects having specific structures.
In the case of a three-dimensional object having a disc portion 202 between upper and lower cylindrical portions 201a, 201b as shown in FIG. 1, when the stereolithographic operation is carried out on a layer basis from the lower end of the cylindrical portion 201a, overhand portions are formed at the disc portion 202 because the diameter of the disc portion 202 is larger than that of the lower cylindrical portion 201a. 
In this case, if the stereolithographic operation is carried out on the overhand portions without using any support, there would occur such a problem that the disc portion 202 is formed so as to hang down or obliquely extend during the stereolithographic operation, and thus it is difficult to design the disc portion in a horizontal disc structure. Therefore, it is difficult to manufacture a three-dimensional object having desired shape and dimension.
In order to solve this problem, a separate support 203 as shown in FIGS. 2A and 2B is disposed in a stereolithographic bath and the stereolithographic operation is carried out while the overhand portions are supported by the support 203 (the support basing method). Here, FIG. 2A is a longitudinal sectional view of a desired three-dimensional object supported by a support when the stereolithographic operation is carried out, and FIG. 2B is a plan view taken from the lower side of the stereolithographically formed object.
Alternatively, in order to solve the above problem, the stereolithographic operation is carried out while a support portion 204 as shown in FIGS. 3A, 3B is formed integrally with the desired three-dimensional object to prevent the overhand portions from hanging down or being deformed (the support attaching method). Here, FIG. 3A is a longitudinal sectional view showing a desired three-dimensional object and a support which is integrally formed with the object, and FIG. 3B is a plan view taken from the lower side of the stereolithographically formed object.
Further, in the case of a three-dimensional object having a central joint plate portion 205, right and left leg portions 206 and 207 which are different in length and extend downwardly from the central joint plate portion 205, and right and left arm portions 208 and 209 extending upwardly from the central joint plate portion 205 as shown in FIG. 4A, the stereolithographic operation is started from the lower end of the longer leg portion 206 in a stereolithographic bath 212 in which liquid photohardenable resin is put as shown in FIG. 4B, and at the time when the height of the leg portion 206 reaches the position corresponding to the lower end of the shorter leg portion 207 as shown in FIG. 4C, the stereolithographic operation is carried out on both the right and left leg portions 206 and 207 at the same time. In this case, a thin-layer portion (photohardened resin layer) 207a constituting the shorter leg portion 207 is not joined to a thin-layer portion (photohardened resin layer) 206a constituting the longer leg portion 206. In addition, the thin-layer portion 207a is not mounted on a mount table, but floated on the liquid photohardenable resin, so that it is liable to be moved. Therefore, the distance between the thin-layer portions 206a and 207a cannot be kept to the proper value in design.
Therefore, in order to avoid this disadvantage, the conventional stereolithographic technique has generally used a method in which as shown in FIG. 4D (longitudinal sectional view) and FIG. 4E (plan view taken from the upper side), a support portion 210 for joining the thin-layer portion 207a to the thin-layer portion 206a is formed simultaneously with the start of the stereolithographic formation of the thin-layer portion 207a of the shorter leg portion 207 (i.e., the support attaching operation is carried out), thereby manufacturing a three-dimensional object having the support portion 210 as shown in FIG. 4F.
In the case of the support basing method, there is required a cumbersome work for forming a support in advance and disposing it in a stereolithographic bath. In addition, it is required that the shape and dimension of a support which is suitable to smoothly prevent hang-down and deformation at an overhang portion are designed in advance and the support is disposed at a proper position, so that great skill is required for the design and use of the support. Further, a support contact mark is liable to remain at a portion on the surface of the three-dimensional object thus formed at which the object was supported by the support. Therefore, the three-dimensional object thus formed has a defective appearance, and a repair treatment of polishing and smoothening the defective portion is required if occasion demands.
In the case of the support attaching method, there is required a cumbersome work for cutting the support portion integrally formed with the three-dimensional object after the stereolithographic operation is completed, thereby removing the undesired support portion. In addition, in order to prevent the appearance of the three-dimensional object from being defective due to the cutting of the support portion, it is necessary to take the shape, size and mount position of the support portion into sufficient consideration, so that sufficiently great skill is required for the support attaching method. Further, when the support portion is removed, it is necessary to remove the support portion while the portion serving as the support portion in the three-dimensional object is sufficiently discretely discriminated from the other portions constituting the desired three-dimensional object (target object). Therefore, if a worker is not skilled to the extent that he/she can understand CAD data, drawings of parts, etc., it is more difficult to perform the removing work of the support portion.
In order to solve the above problems of the conventional stereolithography technique, Japanese Laid-open Patent Application No. Sho-63-72525 discloses a method in which solidifying material such as wax or the like is used as a second material together with a first material of liquid photohardenable resin and a three-dimensional object is optically (stereolithographically) formed while hang-down and deformation at overhand portions, etc. are prevented by the solidifying material.
According to this method, the solidifying second material functions as a support material for supporting a thin layer of photohardened photohardenable resin to prevent the hang-down, the deformation, etc. at the overhang portions, etc. However, in the stereolithographic method disclosed in the above publication, the second material for supporting the shape of an object being stereolithographically formed is separately required together with photohardenable resin with which a desired three-dimensional object is formed. In addition, use of the second material adds the normal process with a step of sucking unhardened photohardenable resin after the light irradiation step is carried out. Further, it further adds many other steps such as a step of coating the solidifying second material in empty portions occurring due to the suction of the unhardened photohardenable resin, a step of polishing and flattening the upper surface of the solidified second material to enhance the dimensional precision in height direction, etc. As a result, the stereolithographic work is extremely complicated, and much labor and time are required to complete the stereolithographic process, so that the stereolithographic apparatus is complicated in construction, scaled up in size and increased in price.
Furthermore, if the second material such as wax or the like coated on the photohardened layer is not sufficiently removed in the flattening and polishing step and thus remains on the photohardened layer, the second material such as wax or the like would be interposed between the photohardened layer and a next photohardened layer laminated thereon, so that the adhesion between the photohardenable layers is disturbed, the laminated photohardenable layers are liable to be peeled off each other and the strength of the three-dimensional object thus formed is lowered.
Still furthermore, photohardenable resin used in the stereolithography technique is generally expensive, and thus unhardened photohardenable resin which has not been photohardened (subjected to the photohardening treatment) has been generally withdrawn and reused after the three-dimensional object is manufactured. However, in the above stereolithographic method disclosed in the above publication, a lot of the second material such as wax or the like is contaminated in unhardened photohardenable resin, and thus it is required to reuse the unhardened photohardenable resin for the stereolithographic process after the second material is perfectly removed from the unhardened photohardenable resin. Therefore, much labor and much cost are needed to purify, withdraw and reuse the photohardenable resin.
Therefore, an object of the present invention is to provide stereolithographic apparatus and method which can solve the above problems of the conventional technique, and can perform plane-exposure with a simple construction.
Another object of the present invention is to provide stereolithographic apparatus and method which can easily form a photohardened resin layer having no uneven surface (i.e., flat surface) in a stereolithographic process.
Other object of the present invention is to provide stereolithographic apparatus and method in which even when a three-dimensional object having a complicated shape such as overhang portions, separately-mounted portions, plural leg portions different in length, uneven portions or the like is manufactured, a desired three-dimensional object can be simply and smoothly manufactured without separately disposing any support in a stereolithographic bath and without forming any support portion serving as a support integrally with a three-dimensional object itself (i.e., without support-attaching).
Further, other object of the present invention is to provide stereolithographic apparatus and method which can optically form a three-dimensional object having a complicated shape such as overhang portions, separately-mounted portions, plural leg portions different in length, uneven portions or the like smoothly and in a short time without any second material such as wax and with only photohardenable resin by a simple process and a simple apparatus.
In order to attain the above objects, according to a first aspect of the present invention, there is provided a stereolithographic apparatus for irradiating light to an unhardened photohardenable resin layer on the basis of data on stereolithography to optically form a desired three-dimensional object, which is characterized by comprising: means for forming a mask on a light-transmissible member on the basis of stereolithographic data for one layer of photohardenable resin; means for forming an unhardened resin layer of photohardenable resin; means for disposing the light-transmissible member having the mask on the unhardened resin layer while the light-transmissible member is brought into close contact with the unhardened resin layer, or disposing the light-transmissible member having the mask above the unhardened resin layer; exposing means for exposing the unhardened resin layer to light through the mask to harden the photohardenable resin of the unhardened resin layer; and
evacuating means for evacuating the light-transmissible member from the hardened photohardenable resin layer after the photohardenable resin of the unhardened resin layer is exposed to light, the desired three-dimensional object being formed by repeating the stereolithography using the respective means.
According to the first aspect of the present invention, since the mask is brought into close contact with the unhardened photohardenable resin layer in the plane-exposing operation, the surface of the hardened resin layer can be flattened. Accordingly, no treatment on the surface of the hardened resin layer after the exposing operation is required, and thus the stereolithographic process can be easily performed.
According to a second aspect of the present invention, there is provided a stereolithographic apparatus for irradiating light to an unhardened photohardenable resin layer on the basis of data on stereolithography to optically form a desired three-dimensional object, which is characterized by comprising: means for forming a mask on a light-transmissible member on the basis of stereolithographic data for one layer of photohardenable resin; photohardenable resin supply/forming means for successively supplying photohardenable resin of one layer to form an unhardened resin layer of photohardenable resin; a film having light transmission which is attached onto the unhardened resin layer so as to cover the unhardened resin layer in close contact with the unhardened resin layer; means for disposing the light-transmissible member having the mask on the film while the light-transmissible member is brought into close contact with the film, or disposing the light-transmissible member having the mask above the film; exposure means for exposing the unhardened resin layer to light through the mask to harden the photohardenable resin of the unhardened resin layer; and evacuating means for evacuating the light-transmissible member and the film from the hardened photohardenable resin layer after the exposure by the exposure means, the desired three-dimensional object being formed by repeating the stereolithography using the respective means.
According to the second aspect of the present invention, the film is attached onto the unhardened photohardenable resin layer with being stretched in the plane-exposure operation, whereby the unhardened photohardenable resin layer is held and no photohardenable resin flows out through the gap between the unhardened photohardenable resin layer and the film. Further, since the film is brought into close contact with the unhardened photohardenable resin layer during the plane-exposing operation, the surface of the resin layer after photohardened is flattened, so that no treatment on the surface of the resin layer after photohardened is required and thus the stereolithographic operation can be easily performed.
According to a third aspect of the present invention, there is provided a stereolithographic apparatus for irradiating light to an unhardened photohardenable resin layer on the basis of stereolithographic data to harden the photohardenable resin layer and repeating the light-irradiating operation for subsequent unhardened photohardenable resin layers in turn to optically form a desired three-dimensional object, which is characterized by comprising: means for forming a mask on a light-transmissible member on the basis of stereolithographic data for one layer of photohardenable resin; a stereolithographic table for mounting photohardenable resin thereon; coating means for successively coating photohardenable resin on the table to form each unhardened photohardenable resin layer; film attaching means for attaching a film having light transmission onto the unhardened photohardenable resin layer; means for superposing the light-transmissible member having the mask on the film or disposing the light-transmissible member having the mask above the film; exposure means for exposing the photohardenable resin of the unhardened photohardenable resin layer through the mask; and film peeling means for peeling off the film after the unhardened photohardenable resin layer is exposed, the desired three-dimensional object being formed by repeating the stereolithography using the respective means.
Further, according to a fourth aspect of the present invention, there is provided a stereolithographic method for irradiating light to an unhardened photohardenable resin layer on the basis of stereolithographic data to harden the photohardenable resin layer and repeating the light-irradiating operation on subsequent unhardened photohardenable resin layers in turn to optically form a desired three-dimensional object, which his characterized by comprising: a step of forming a mask on a light-transmissible member on the basis of stereolithographic data of one layer of photohardenable resin; a step of forming one unhardened photohardenable resin layer; a step of disposing the light-transmissible member having the mask on the unhardened photohardenable resin layer while the light-transmissible member is brought into close contact with the unhardened photohardenable resin layer, or disposing the light-transmissible member having the mask above the unhardened photohardenable resin layer; a step of exposing the unhardened photohardenable resin layer to light through the mask; and a step of evacuating the light-transmissible member after the unhardened photohardenable resin layer is exposed to light, a series of the steps being repeated in this order to form a desired three-dimensional object.
Still further, according to a fifth aspect of the present invention, there is provided a stereolithographic method for irradiating light to an unhardened photohardenable resin layer on the basis of stereolithographic data to harden the photohardenable resin layer and repeating the light-irradiating operation on subsequent unhardened photohardenable resin layers in turn to optically form a desired three-dimensional object, which is characterized by comprising: a step of forming a mask on a light-transmissible member on the basis of stereolithographic data of one layer of photohardenable resin; a step of forming an unhardened photohardenable resin layer on a stereolithographic table; a step of attaching onto the unhardened photohardenable resin layer a film having light transmission which holds the unhardened photohardenable resin layer; a step of disposing the light-transmissible member having the mask on the film while the light-transmissible member is brought into close contact with the film, or disposing the light-transmissible member having the mask above the film; a step of exposing the unhardened photohardenable resin layer to light through the mask; and a step of evacuating the light-transmissible member and the film after the unhardened photohardenable resin layer is exposed to light, a series of the steps being repeated in this order to form a desired three-dimensional object.
In order to attain the above objects, the inventors of this application have made further various experiments and reviews repetitively, and as a result they have found out that a three-dimensional object having complicated shape and structure with overhang portions, separately-mounted portions, plural leg portions different in length, uneven portions or the like can be simply and smoothly manufactured with high precision without occurrence of hang-down, deformation and displacement at the above portions neither by disposing a separate support in a stereolithographic bath nor by attaching a support to a three-dimensional object itself, and further without any second material such as wax or the like as support material under the condition that a photohardenable resin composition which has a melting temperature ranging from 5 to 90xc2x0 C. before it is photohardened and is reversibly shifted from liquid-phase to solid-phase or from solid-phase to liquid-phase with the melting temperature at the boundary between these phases is used as photohardenable resin. When a photohardenable resin is exposed to light to form a photohardened layer, the above photohardenable resin composition constituting the same surface as a photohardened layer which has been already formed and is just below a photohardened layer to be next formed is kept at a temperature less than the melting temperature thereof to keep the photohardenable resin composition solid, and then a layer of photohardenable resin composition is supplied onto the solid surfaces of the solid photohardenable resin composition layer and the photohardened layer and exposed to light while the layer thus supplied is supported by the solid surfaces of the solid photohardenable resin composition layer and the photohardened layer to further form a photohardened layer.
Further, the inventors of this application has also found out that in the stereolithographic operation, a photohardenable resin layer to be supplied onto the surface of a solid photohardenable resin composition layer may be supplied in any one of liquid and solid states, and the photohardenable resin layer thus supplied may be photohardened in any one of liquid and solid states.
Still further, the inventors of this application has also found out that when the stereolithographic operation is carried by the above method using the photohardenable resin composition having the melting temperature ranging from 5 to 90xc2x0 C. before it is photohardened, if the photohardenable resin composition is heated to be kept at a temperature above the melting temperature thereof after the stereolithographic operation is completed or at some midpoint of the stereolithographic operation, the photohardenable resin composition which is not subjected to photohardening (i.e. unhardened resin composition) becomes liquid, so that it can be easily and smoothly separated from a three-dimensionally object formed by the photohardening, and also the unhardened photohardenable resin composition thus separated can be directly reused for the subsequent (next) stereolithographic operation because it does not contain any second material such as wax or the like.
Still further, the inventors of this application has also found out that the unhardened photohardenable resin composition can be separated from the three-dimensional object formed by the photohardening not only by using the above heat-melting method of heating and melting the solid unhardened photohardenable resin composition, but also by using a method of dissolving the solid unhardened photohardenable resin composition with solvent.
Accordingly, according to a sixth aspect of the present invention, there is provided a stereolithographic method including a photohardened layer forming step of exposing a photohardenable resin composition layer to light controlled on the basis of stereolithographic data to harden the photohardenable resin composition layer, thereby forming a photohardened layer having predetermined pattern and thickness, and a photohardened layer forming/laminating step for forming a photohardenable resin composition layer on the photohardened layer formed in said photohardened layer forming step, exposing the photohardenable resin composition layer to light controlled on the basis of stereolithographic data to laminate a subsequent photohardened layer on the preceding photohardened layer, and repeating the lamination of a subsequent photohardened layer on a preceding photohardened layer until a desired three-dimensional object is obtained, which is characterized in that the photohardenable resin composition has a melting temperature ranging from 5 to 90xc2x0 C. when unhardened, and in at least a part of the photohardened layer forming/laminating process, under a state that an unhardened photohardenable resin layer forming the same surface as a photohardened layer which has been already formed is kept solid at a temperature less than the melting temperature, a layer of photohardenable resin composition is formed on the surface of the solid photohardenable resin composition layer, and the photohardenable resin composition layer is exposed to light controlled on the basis of stereolithographic data to laminate a photohardened layer on the solid photohardenable resin composition layer.
Further, according to a seventh aspect of the present invention, there is provided a stereolithographic apparatus comprising: supply means of successively supplying a layer of photohardenable resin composition onto a mount table or a photohardened layer formed by hardening photohardenable resin composition; stereolithography means having a light irradiation device for repeating formation/lamination of photohardened layers each having predetermined pattern and thickness under control until a desired three-dimensional object is formed; and temperature adjusting means for keeping the temperature of the photohardenable resin (composition): to a temperature less than the melting temperature thereof.